Abstract
Cholesterol is a key cell membrane component and precursor of steroid hormones. The maternal cholesterol is an important exogenous cholesterol source for the developing embryos and its transportation is mediated by ABCA1 and SR-BI. Here we reported that during the peri-implantation period in pigs, ABCA1 was expressed by uterine luminal epithelium (LE) and interestingly, its expression was more abundantly in LE on mesometrial side of uterus. However, SR-BI was expressed primarily by LE, glandular epithelial cells (GE) and trophoblast cells (Tr). During the placentation period, the expression levels of ABCA1 and SR-BI proteins at epithelial bilayer and placental areolae were significantly higher in Chinese Meishan pigs compared to Yorkshire pigs. Consisitently, mRNA levels of HMGCR, the rate-limiting enzyme for cholesterol synthesis, were significantly higher in Meishan placentas than in Yorkshire placentas. Our findings revealed the routes of transplacental cholesterol transport mediated by ABCA1 and SR-BI in pigs and indicated that ABCA1 related pathway may participate in anchoring the conceptus to the mesometrial side of uterus. Additionally, an ABCA1 dependent compensatory mechanism related to the placental efficiency in response to the smaller placenta size in Meishan pigs was suggested.
Highlights
The efficiency of maternal-fetal nutrients transport is closely correlated with the rate of embryo implantation and the degree of fetal development[1,2,3]
Due to the fact that cholesterols serves as the ultimate precursor for the biosynthesis of all steroid hormones including the estrogen, the cholesterol is critical for the conceptus development and successful implantation in pigs[21,22]
We found that the level of Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) mRNA was very low in the Yorkshire conceptuses during the peri-implantation period
Summary
The efficiency of maternal-fetal nutrients transport is closely correlated with the rate of embryo implantation and the degree of fetal development[1,2,3]. Further investigations illustrated that the difference in degree of the piglet development before and at birth between Meishan and western breeds is mainly due to the difference in placental efficiency. Cholesterol is required for the synthesis of sonic Hedgehog (SHH) proteins, a secreted molecule necessary for organogenesis[24] Both the conceptus at rapidly trophoblastic elongation stage and the growing fetus at later stage of pregnancy need a large amount of cholesterol for cell differentiation and proliferation. ABCA1, a member of the ABC transporter superfamily, is a membrane spanning protein that performs cholesterol and phospholipids unidirectional efflux to lipid-poor apolipoprotein A-I (apoA-I) to form precursor of high density lipoprotein (HDL)[30]. SR-BI is dynamically expressed in the maternal-fetal interface during pregnancy and was demonstrated to facilitate maternal-fetal cholesterol transport[39,40]
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